Studies will be performed on: 1. Interaction of acetoacetyl-CoA and beta-hydroxybutyryl-CoA with rat liver pyruvate carboxylase. 2. Effects of various portions of the CoA molecules on the rate of inactivation of rat and chicken liver pyruvate carboxylases by trinitrobenzenesulfonate. 3. Effect of substrates and cofactors on the rate of formation of the trinitrophenylated enzyme. 4. Purification and characterization of pyruvate carboxylases from Tenebrio molitor, Rana catesbiana, and rat brain.